For effective bleaching with hydrogen peroxide, the latter must be converted into a species having more bleaching activity. One possibility for generating activated peroxy compounds is the use of peracid precursors, so-called “bleach activators” such as TAED, that are converted by perhydrolysis into the active species.
A further possibility for generating activated species is enzymatically catalyzed perhydrolysis of carboxylic acid esters or nitrile compounds using perhydrolases.
Lastly, it is also known to use bleach catalysts to generate activated species, a “bleach catalyst” being understood as a substance that can improve the bleaching performance of hydrogen peroxide on a bleachable material without itself participating stoichiometrically in the reaction.
The use of bleach catalysts has the advantage, as compared with the other bleach activation methods, that substoichiometric quantities of the compound are sufficient, with the result that space and weight can be saved in the formulation of the bleach-containing product. In addition, the reduction in weight, especially in the context of washing and cleaning applications, is also associated with the advantage that less material is discharged into the environment, which is particularly advantageous for ecological reasons. Transportation and packaging costs can also be reduced as a result.
Consideration must also be given to the fact that premature hydrolysis can occur when bleach activators such as nitriles or TAED are used in the presence of water, whereas this problem can be very largely eliminated with the use of bleach catalysts. Furthermore, the production of acids that occurs in the context of noncatalytic bleach activation based on peracids causes a shift in pH that can have an unfavorable effect on bleaching performance. In addition, the bleaching performance of most bleach activators at low temperatures is often unsatisfactory.
For the reasons cited above, the use of bleach catalysts is of particular interest as compared with the other techniques for bleach activation, so that a demand exists in principle for novel bleach catalysts.
Bleach catalysts that have been described are, in particular, metal complexes of organic ligands such as salenes, saldimines, tris[salicylideneaminoethyl]amines, monocyclic polyazaalkanes, cross-bridged polycyclic polyazaalkanes, terpyridines, and tetraamido ligands. A disadvantage of the metal complexes just described is, however, that they either they do not possess sufficient bleaching performance especially at low temperature, or that, with sufficient bleaching performance, undesirable damage occurs to colors and, in some cases, also to textile fibers.
N-Alkyl-2,2′-imino-bis-(8-hydroxyquinoline)-metal complexes are already described in the existing art. DE19825737, for example, describes zinc, magnesium, aluminum, gallium, indium, and lutetium complexes of such ligands, and the use of said complexes in an electroluminescent arrangement. Agustin et al. (J. Org. Chem. 592 (1999) 1-10) describe germanium and tin complexes of N-methyl-2,2′-imino-bis(8-hydroxyquinoline), and Fagan et al. (J. Am. Chem. Soc. 122 (2000) 5043-5051) describe the copper complex of this ligand and an investigation of its property of phenoxylating 2-bromo-4,6-dimethylanilines. Stockwell et al. (J. Am. Chem. Soc. 121 (1999) 10662-10663) investigate the influence of N-methyl-2,2′-imino-bis(8-hydroxyquinoline) on the expression of different genes in Saccharomyces cerevisiae, and additionally investigate the complex-forming constants of this ligand with reference to various metal ions.
Wang et al. (inorganica Chimica Acta 321 (2001) 215-220) describe ruthenium complexes of bis(8-hydroxyquinolin-2-yl)ether. DE2650764 describes the use of 2,2′-methylene-bis(8-hydroxyquinoline) as a polyfunctional coupler for the development of color images.
Use of the ligands and metal-ligand complexes as bleach catalysts, or as an additive for washing and cleaning agents, is not described in the aforesaid documents.